As we all know the lm4 comes standard with some play between the uppers. It wasnt really ever a bother to me but since i was bored and had an idea. I thought i would try it just to see if my concept worked.

When looking carefully at how the upper and lower wobble i determined that it may be due to too much space left between the upper and lower. So, i went to my box of rc paint equipment, and found myself some pactra trim tape. Remember i am just trying to see if my concept will work in action.

Using the thickness close enough to the thickness of the receiver walls, i just simply applied the tape like so:

Make sure to wipe off any oil where you apply the tape or else it wont stick.

This is by no means a permanent modification, but just testing a hypothesis.

The results were positive! Using this thin trim tape, the receiver wobble is gone.

So by filling in the gap between the upper an lower, you can cut the wobble to essentially nothing.

Aluminum tape may also be a contender here for it is fairly thin and may have better adhesion. Duck tape will probably be too thick because if you put in too thick of a spacer the rear pin will not go all the way home.

Maybe even a feeler gauge could fix the wobble if it is thin enough? Throw out some ideas people and give it a shot. This is what i tried and it worked. Now i just have to see how long it lasts.

The only wobble left to fix would be the handguard wobble, and the carry handle rail wobble, which im too lazy to fix that right now.

Anyone try the magic pin from Ra-tech yet? Or the g&p pin that is similar to the magic pin? I have the g&p pin in my other gbbr's and they work great..eliminates ALL wobble. I was going to try the magic pin in the LM4 but I've got some rs takedown pins otw that I want to install (its got grim reaper logo engraved on them) maybe those will get rid of wobble too if the diameter is bigger I think I can make it work.
Sent from my DROID2

Pretty much out of the box. I think its just the dimensions of the receiver that have allowed for the wobble.

Did any of you try to see if the pin would fit in the hole in the upper by itself? Just to see if that is the case, where the upper hole is larger than the lowers. That way you can narrow down the correct size needed to see if the wobble will stop.

I used this idea to eliminate my wobble completely. I was very surprised that although I don't think it's the source of the problem, my wobble was eliminated 100%. I used one layer of duct tape, and one layer of packaging tape on top of that. It's not visible at all from outside of the gun, not even slightly. I think it'd be a really good idea if someone had the resources, to make pre-cut patterns of tape to solve this problem. Too describe how much wobble I can feel, I might as well be trying to feel receiver wobble in a solid brick.

Anyone try the magic pin from Ra-tech yet? Or the g&p pin that is similar to the magic pin? I have the g&p pin in my other gbbr's and they work great..eliminates ALL wobble. I was going to try the magic pin in the LM4 but I've got some rs takedown pins otw that I want to install (its got grim reaper logo engraved on them) maybe those will get rid of wobble too if the diameter is bigger I think I can make it work. Sent from my DROID2

I personally do NOT recommand those. If you tighten them, it makes the receiver tight, but if you split receiver while it's tighten, you WILL break the upper receiver. Broke one, took 6 months to get a replacement upper.

It worked! I used 2 layers of aluminum tape(after one layer it was still a tad wobbly). However now the back receiver pin is a little harder to get in but still doable with just my hands. Also the tape is very slightly visible( I probably could have done a better job).
Thanks for the advice!

Of the six different .223 and two .22LR AR-15 platforms I own, except for the matched set from Sun Devil, have a little bit of wobble between the upper and lower receivers. The LM4 is no exception. The wobble is part of the original design envisioned by Mr. Stoner. It does not affect function, accuracy, or reliability. All these little tricks to solidify the connection between the upper and lower units are an exercise in diminishing returns.

Expanding on AzizaVFR's comments: The use of anything flexible (gimmicks like the (In)AccuWedge or an earplug under the rear takedown pin)to stop receiver slop or "wobble" do not increase accuracy and can degrade the accuracy of the 5.56mm versions of this rifle as the flexibility does not place the parts in the same location for every shot.

The little bit of receiver slop is consistently removed if there is nothing flexible pushing against your hold. This degrade of accuracy is unlikely to be a major problem in airsoft but no help either. It's wasted effort on your part for either real or airsoft -- but it doesn't stop the sale of Accuwedges.

True match grade M16/AR15 rifles, like those that compete at Camp Perry, are machined/bedded to very exact tolerances with nothing flexible between the receivers. Note these are also only expected to shoot about 100 rounds in the course of a day.

It's starting to be more prominent since I've broken the gun down multiple times. It effects nothing but it pisses me of when the entire top receiver wobbles while running. Anyone have good results using a magic pin. Or is the alumi tape the best bet. Mine has a noticeable gap on either side once it tilts to either

What i found worked best was AR-15 shims. I placed just one in the front and one in the rear pins and fixed mine altogether. My wobble had enough the bolt catch didn't function., and now works flawlessly again. Feels good an solid like a RS now. here is a link to the shims. Cost about $23 with shipping. There's 10 to a pack.